connections java.net.BindException: Address already in use_解决方案

一、问题描述

在Linux服务器（CentOS7系统）中配置并启动JMeter远程监控服务器资源所需的ServerAgent目录下的 startAgent.sh 文件时，系统出现异常提示，如

[root@localhost ServerAgent-2.2.3]# ./startAgent.sh
INFO    2018-12-15 10:29:17.634 [kg.apc.p] (): Binding UDP to 4444
ERROR   2018-12-15 10:29:17.686 [kg.apc.p] (): Can't accept UDP connections
java.net.BindException: Address already in use
        at sun.nio.ch.Net.bind0(Native Method)
        at sun.nio.ch.Net.bind(Net.java:433)
        at sun.nio.ch.DatagramChannelImpl.bind(DatagramChannelImpl.java:691)
        at sun.nio.ch.DatagramSocketAdaptor.bind(DatagramSocketAdaptor.java:91)
        at kg.apc.perfmon.PerfMonWorker.listenUDP(PerfMonWorker.java:144)
        at kg.apc.perfmon.PerfMonWorker.startAcceptingCommands(PerfMonWorker.java:107)
        at kg.apc.perfmon.AgentTool.processParams(AgentTool.java:72)
        at kg.apc.cmdtools.PluginsCMD.processParams(PluginsCMD.java:63)
        at kg.apc.cmdtools.PluginsCMD.processParams(PluginsCMD.java:23)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

二、问题分析

从以上抛出的异常信息中提取关键的提示信息：
"Can't accept UDP connections
java.net.BindException: Address already in use"

分析：ServerAgent默认开始的是4444端口，提示“不能接收UDP连接，地址已在使用中”，很可能是该端口已被占用，需要修改为新的端口号再启用or先暂停该端口对应的进程，然后再启用ServerAgent服务

三、解决方案

方式1：先暂停4444端口，再启用ServerAgent服务

查询4444端口当前对应的进程：lsof -i:4444

[root@localhost ServerAgent-2.2.3]# lsof -i:4444
COMMAND    PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
java    104069 root   18u  IPv6 3997358      0t0  UDP *:krb524
java    104069 root   19u  IPv6 3997549      0t0  TCP *:krb524 (LISTEN)

关闭指定PID号码的进程（4444端口进程）：kill -9 104069
此时，亦可正常启用ServerAgent服务，如下：

[root@localhost ServerAgent-2.2.3]# kill -9 104069
[root@localhost ServerAgent-2.2.3]# lsof -i:4444
[root@localhost ServerAgent-2.2.3]# ./startAgent.sh
INFO    2018-12-15 10:41:51.043 [kg.apc.p] (): Binding UDP to 4444
INFO    2018-12-15 10:41:52.059 [kg.apc.p] (): Binding TCP to 4444
INFO    2018-12-15 10:41:52.066 [kg.apc.p] (): JP@GC Agent v2.2.3 started

方式2：修改ServerAgent端口，再启用ServerAgent服务

./startAgent.sh –udp-port 0 –tcp-port xxxx （"xxxx" 为新端口号，如：4567）
./startAgent.sh –udp-port 0 –tcp-port 4567